Why the tides rise and fall

Grade 9 Science Worksheet

Circle the best answer.

1. Read this first

   Table, Tide table for a beach (model data), with columns Tide, Time, Height (m)

   High, 5:10 a.m., 1.8; low, 11:22 a.m., 0.3; high, 5:35 p.m., 1.7; low, 11:47 p.m., 0.4.

2. 1.

   Using the tide table, about when will tomorrow's first high tide come, by Esme's math?

   • About 4:20 a.m.
   • About 5:35 a.m.
   • About 5:10 a.m., the same as today
   • About 6:00 a.m.
3. 2.

   How long is it from the 5:10 a.m. high tide to the 5:35 p.m. high tide, by Jun's math?

   • 12 hours
   • 24 hours 50 minutes
   • 12 hours 25 minutes
   • 6 hours 12 minutes
4. 3.

   Tidal force ∝ mass ÷ distance³; Sun 27 million times the mass, 390 times the distance. NOAA: the Sun has 27 million times the Moon's mass but is 390 times as far away. Tidal force ∝ mass ÷ distance³. Compare the Sun's tidal force with the Moon's, by Kira's math.

   • About 27 million times stronger
   • About 69,000 times stronger
   • About 177 times stronger
   • About 0.46, under half
5. 4.

   The Sun's pull on Earth (long) and its tidal effect (short). The Sun pulls on Earth about 177 times harder than the Moon, yet its tides are about half as big. Why, by Milo's reading (NOAA)?

   • The Moon has more mass than the Sun
   • Tides depend on distance cubed, which shrinks the Sun's effect
   • Tides follow gravity, which falls as distance squared
   • The Sun's gravity cannot reach the oceans

6. Moon distance (NASA)

   Point	Distance (km)
   perigee	363,300
   apogee	405,500

7. 5.

   The Moon is 363,300 km away at perigee and 405,500 km at apogee (NASA). How much stronger is its tidal force at perigee, by Noah's math?

   • It is weaker at perigee
   • About 1.39 times stronger
   • About 1.25 times stronger
   • About 1.12 times stronger
8. 6.

   Moon orbit diagram with perigee and apogee marked. When are tidal ranges larger than average, by Pia's reading (NOAA)?

   • On cloudy days
   • In the spring season
   • When the Moon is at perigee, closest to Earth
   • When the Moon is at apogee, farthest away
9. 7.

   Earth's orbit with perihelion marked about January 2. Earth is closest to the Sun about January 2 (NOAA). What happens to the tides then, by Ren's reading?

   • Tidal ranges are a little larger
   • Tides become smaller
   • Spring tides happen in January alone
   • Tides stop for the day
10. 8.

    At full Moon, the Sun and Moon are on opposite sides of Earth. Why is that still a spring tide, by Tala's reading?

    • Opposite sides cancel, so tides are small
    • The Sun's bulge sits across and cancels
    • Full Moonlight lifts the water
    • Their bulges line up along one line and add together
11. 9.

    At first quarter Moon, why are tides moderate (neap), by Zee's reading (NOAA)?

    • The Sun and Moon line up
    • The Moon is closest then
    • It is winter at first quarter
    • The Sun's tide is at a right angle and partly cancels the Moon's
12. 10.

    Moon-phase calendar starting at new Moon on Monday. A spring tide comes with Monday's new Moon. About when is the next spring tide, by Ari's reading?

    • About one week later, at first quarter
    • About two weeks later, at full Moon
    • Next spring
    • About two months later